In U.S. Pat. No. 6,748,224 is described a local positioning system using the radio propagation parameters in a code division multiple access (CDMA) forward link or time division multiple access (TDMA) reverse link to establish a mobile station's position. The mobile station receives pilot channel signals from at least three distinct base stations and records the pseudo-random noise chip offset of the pilot channel signals. This is enough to perform some classical triangulation based on time difference of arrival and requiring no additional signal detection capabilities. Base stations send out pilot channel signals that arrive at a mobile station with a particular phase and at least a predetermined minimum strengths. The mobile station reports back the visible pilot channel signals, their phases and signal strength to the LPS which uses a location non-linear system to estimate the mobile location. Such a LPS can also solve the E911-E112 mobile location problem for wireless CDMA system by determining the position of a person in distress that has a digital cellular phone.
In U.S. Pat. No. 6,385,458 is described a method, a computer program and systems that implement a location service in a mobile communications network to generate a location estimate for a terminal device associated with a user. The proposed method takes a location request, and, with a precision that is dependent on an assigned priority level, estimates the location of a mobile phone.
The two above cited prior arts are two typical prior arts among other dealing with the location of a end user in case of a E911-E112 emergency call. Both prior arts are based on a location measurement system which must be in a correct running mode to be able to forward the required location information. In the case such a location measurement system is in an idle state, the required information cannot be collected which cause serious problem in case of an emergency call. This is a quite hot topic for telecommunications network built on Internet Protocol IP particularly for a premise IP network (indoor or closed network). In that case, all the telecommunications are performed using wired IP terminals or wireless IP terminals. A location of a user inside such indoor IP network can be provided using the access points of the corresponding wireless network infrastructure spread over the closed environment usually matching the campus of a firm or specific organization. In that case, the wireless network infrastructure used for providing telecommunication facilities in a wireless mode through out the campus are also used for locating a user of such an IP terminal. The location can be based on classical triangulation methods or any other location procedure using the access points. Such wireless network infrastructure can however be out of order at least for some finite time interval. Consequently, users inside the environment covered by the wireless network infrastructure and equipped with wireless IP terminals cannot call outside anymore and cannot be located for help. Such interruptions are not so speculative since some wireless network infrastructure are powered such that the access points are powered using the already existing powering facility. And in case of a general powering break out, the wireless network infrastructure will be then in an idle state rendering impossible any location procedure of a user inside the environment covered by that wireless network infrastructure. Such situation is particularly unsatisfactory in case an emergency call is launched using e.g. some IP wired telecommunications terminal. Even more, in the situation of fire, there is no guaranty that the equipment will not be destroyed rendering the use of such telecommunications terminal simply impossible.